Calibration of force based touch panel systems

Abstract

A method and system are provided to correct inaccuracies in touch location determination associated with mechanical distortion of the touch screen. Calibration parameters are provided for a touch screen characterizing an error in an expected touch signal associated with mechanical distortion of the touch screen. A force responsive touch signal having the error is detected and the touch location determined using the calibration parameters to correct the error in the touch signal. The calibration parameters are determined by applying mechanical distortion to the touch screen and characterizing the touch signal error associated with the mechanical distortion. The calibration parameters are produced using the characterization of the touch signal error.

1 . A method for calibrating a touch screen, comprising: 
 applying mechanical distortion to the touch screen;    detecting a force responsive touch signal arising from the mechanical distortion of the touch screen;    characterizing a touch signal error associated with the mechanical distortion; and    producing calibration parameters using the characterization of the touch signal error.    
   
   
       2 . The method of  claim 1 , wherein characterizing the touch signal error associated with the mechanical distortion comprises: 
 applying two or more distortion conditions to the touch screen;    detecting sensor signals corresponding to each distortion condition; and    characterizing the effect of distortion using the sensor signals corresponding to each distortion condition.    
   
   
       3 . The method of  claim 2 , further comprising: 
 determining one or more basic calibration vectors; and    determining one or more distortion corrected calibration vectors using the one or more basic calibration vectors and the sensor signals corresponding to each distortion condition.    
   
   
       4 . The method of  claim 3 , wherein determining the one or more basic calibration vectors comprises calculating the one or more basic calibration vectors from nominal sensor locations and known parameters of the touch screen design.  
   
   
       5 . The method of  claim 3 , wherein determining the one or more basic calibration vectors comprises measuring sensor locations and touch screen parameters.  
   
   
       6 . The method of  claim 3 , wherein determining the one or more basic calibration vectors comprises measuring sensor signals corresponding to one or more known forces applied at one or more known locations on the touch screen.  
   
   
       7 . The method of  claim 3 , wherein determining the one or more basic calibration vectors comprises applying known forces in the vicinity of each touch sensor location and measuring the sensor signals responsive to the known forces.  
   
   
       8 . The method of  claim 2 , wherein applying the two or more distortion conditions comprises: 
 applying a zero distortion as a first distortion condition; and    applying a non-zero distortion as a second distortion condition.    
   
   
       9 . The method of  claim 2 , wherein applying the two or more distortion conditions comprises: 
 applying a first non-zero distortion condition as a first distortion condition; and    applying a second non-zero distortion condition as a second distortion condition.    
   
   
       10 . The method of  claim 9 , wherein the first distortion condition has an effect opposite to an effect of the second distortion condition.  
   
   
       11 . The method of  claim 2 , wherein applying two or more distortion conditions to the touch screen comprises applying the distortion conditions to the touch screen at the same time that known forces are applied to the touch screen.  
   
   
       12 . A touch screen calibration system, comprising: 
 a mechanical distortion system for applying mechanical distortion to the touch screen;    a detection system for detecting force responsive sensor signals arising from the mechanical distortion; and    a processor, coupled to the detection system, and receiving the sensor signals detected by the detection system, the processor configured to detect a force responsive touch signal arising from the mechanical distortion of the touch screen, characterize a touch signal error associated with the mechanical distortion of the touch screen, and produce calibration parameters using the characterization of the touch signal error.    
   
   
       13 . The system of  claim 12  wherein the mechanical distortion system is configured to apply two or more mechanical distortion conditions to the touch screen.  
   
   
       14 . The system of  claim 12 , wherein the mechanical distortion applied to the touch screen is torsion.  
   
   
       15 . The system of  claim 13 , wherein the processor is configured to detect sensor signals arising from each mechanical distortion condition, and characterize the touch signal error using the sensor signals arising from each mechanical distortion condition.  
   
   
       16 . The system of  claim 12 , further comprises a force application system for applying known forces to the touch screen, wherein the processor is further configured to determine one or more basic calibration vectors, and determine one or more distortion corrected calibration vectors using the one or more basic calibration vectors and the sensor signals corresponding to each distortion condition.  
   
   
       17 . The system of  claim 16 , wherein the known forces are applied by the force application system in the vicinity of each touch sensor location.  
   
   
       18 . The system of  claim 13 , wherein the mechanical distortion system: 
 applies a zero distortion as a first distortion condition; and    applies a non-zero distortion as a second distortion condition.    
   
   
       19 . The system of  claim 13 , wherein the mechanical distortion system: 
 applies a first non-zero distortion condition as a first distortion condition; and    applies a second non-zero distortion condition as a second distortion condition.    
   
   
       20 . The system of  claim 19 , wherein the first distortion condition has an effect opposite to an effect of the second distortion condition.  
   
   
       21 . The system of  claim 13 , wherein the mechanical distortion system applies two or more distortion conditions at the same time that known forces are applied to the touch screen.  
   
   
       22 . A system for calibrating a touch screen, comprising: 
 means for applying mechanical distortion to the touch screen;    means for detecting sensor signals associated with the mechanical distortion; and    means for calibrating the touch screen to compensate for the mechanical distortion.    
   
   
       23 . The system of  claim 22 , wherein means for applying mechanical distortion to the touch screen comprises means for applying a first and a second torsion to the touch screen.  
   
   
       24 . The system of  claim 22 , wherein means for calibrating the touch screen comprises: 
 means for determining a basic calibration; and    means for calibrating the touch signal using the basic calibration and the detected sensor signals affected by the mechanical distortion.    
   
   
       25 . The system of  claim 24 , wherein means for determining a basic calibration comprises: 
 means for applying known forces to the touch screen;    means for detecting sensor signals responsive to the known forces; and    means for determining basic calibration vectors for the touch screen using the sensor signals responsive to the known forces.    
   
   
       26 . The system of  claim 24 , wherein means for calibrating the touch signal using the basic calibration and the detected sensor signals affected by the mechanical distortion comprises means for determining torsion corrected calibration vectors for the touch screen.  
   
   
       27 . The system of  claim 22 , wherein means for applying mechanical distortion to the touch screen comprises means for applying the distortion conditions to the touch screen at the same time that known forces are applied to the touch screen.  
   
   
       28 . A computer-readable medium configured with executable instructions for causing one or more computers to perform a method of calibrating a touch screen, the method comprising: 
 applying mechanical distortion to the touch screen;    detecting a force responsive touch signal arising from the mechanical distortion of the touch screen;    characterizing a touch signal error associated with the mechanical distortion, the touch signal error arising in a force responsive touch signal; and    producing calibration parameters using the characterization of the touch signal error.